When winding magnetic recording tape onto a reel in a tape cassette it is desirable that the hub have the largest possible diameter, within the constraints of tape length and overall package size. This reduces the amount of tape damage due to flexing or stretching, reduces the tension on the tape caused by smaller winding diameters, and reduces the number of reel rotations necessary to wind or unwind a length of tape.
In video cassettes the maximum length of tape which can be wound onto the reel is determined and limited by the size of the cassette, which must be a standard size to function in standard video tape machines. However, in many cases, less than the maximum amount of tape is needed. In these cases, it is desirable to provide the same diameter reels with a larger hub diameter to achieve the above results. This is the case with video cassettes as well as with other types of tape recording media, such as audio cassettes and data cassettes.
However, providing more than one hub diameter presents significant manufacturing problems, since video cassettes are produced in large volumes, using high speed multicavity injection molding equipment and automated assembly equipment. Many of the advantages inherent in using such equipment are lost if even occasional shutdowns are needed to accommodate changes in the product being produced. Additionally, producing larger-than-standard hub diameters presents other problems, including increased tooling costs. As molds for making complete hubs are complex and expensive, since many hub sizes may be required in relatively small and unpredictable quantities, tooling costs can become prohibitive.
A further problem in producing a series of tape reels which differ only in hub diameter, is the confusion which can arise without a suitable method for quickly identifying the various hub sizes. One common part identification method is color coding. However, it is often not convenient, economical, or even possible, to provide the desired color and materials having the mechanical and molding properties for making complete hubs.
One well known method of accommodating product variety while still retaining the advantages of high volume production equipment is modular product design. Tape reels having a larger than standard hub diameter can be made by providing a circular insert which fits over the standard, presumably smallest, hub.
U.S. Pat. No. 4,083,508 discloses a circular insert for reducing the tape capacity of a reel used in data recording. However, this insert does not lend itself to automated assembly, as sonic welding must be used to attach the insert to the reel flange. Sonic welding is time consuming, requires special equipment and proper part design, and may not be applicable to all materials that might otherwise be suitable for use. Additionally, this insert lacks any system to secure the tape to the reel.
In U.S. Pat. No. 4,760,972, a two-part reel construction is disclosed. In this reel, the two parts are concentric circular components. The two-part construction yields a more precisely shaped hub which reduces misalignment and subsequent damage to the tape. However, this hub design requires that additional parts be used in every reel, not just those requiring larger hub diameters. This does not allow a choice of hub diameters in automatically assembled tape cassettes.
U.S. Pat. No. 4,176,804 is directed to a reel construction in which the hub is formed of two separate semicircular halves which can be separate from the reel flanges. This reel does not increase the choice of hub diameters, but rather provides a flexible core which does not stretch the tape when a large mount of tape is tightly wound onto the reel. Also, the two-part construction of this insert adds unnecessarily to the complexity of any automated assembly.
None of the known hub designs provides a reel insert for use with otherwise complete tape reels which permits tape reels having a number of different possible hub diameters to be made using the same automated assembly equipment, with a minimum of changeover, downtime, and startup time required to change from one hub diameter to another. None of these designs produces reel hubs with a plurality of different diameters such that the hub which is produced in the largest volumes has the fewest parts.